1. Technical Field
The present invention relates to dual battery electrical systems for vehicles operating in a stop/start mode.
2. Background Art
In modern vehicles a large number of electrical loads are required to be powered by one or more batteries of the vehicle. These loads generally include a starter motor used to crank the engine and may include other systems whose operation is essential for starting the vehicle, such as security systems and the engine management system. It is clearly undesirable for the battery or batteries to be drained by powering other loads such as the radio, lights, phone charger or in car entertainment systems when the vehicle ignition is off so that when the vehicle needs to be started, the battery does not have enough power to drive the starter motor. In order to avoid this situation, it is known to have a dual battery system in which two batteries are used to power a vehicle—one of the batteries being dedicated to the starter mechanism. The dedicated starter battery is switched off after it is used such that it is not in use once the vehicle has been started. Therefore the power of the battery dedicated solely to the starting mechanism is not available to power any other load while driving.
Most known vehicles have an ignition switch in the form of an ignition key which is user operated and arranged to allow a user to switch the vehicle system between an OFF state (in which the engine is off and all other electrically powered vehicle systems are also switched off), an ON state (in which the engine is running and vehicle systems are turned on) and a START state (when the ignition key is turned to crank an engine in order to provide power to a starter motor, for example).
Some newer vehicles also operate in a PAUSE state. The PAUSE state has been developed in order to provide more fuel efficient vehicle systems. The PAUSE state usually operates by virtue of a vehicle controller detecting that the vehicle has become stationary (e.g. stopped at traffic lights) and, in response, shutting down the vehicle engine until the driver wishes to move the vehicle again. This type of operation is commonly known as “stop/start” operation. In some such vehicles, certain predetermined conditions have to be met before the vehicle system enters the PAUSE state, for example a clutch may need to be raised and the transmission mechanism must be neutral. There may also be a requirement for a predetermined time period to elapse while the vehicle is stationary before the PAUSE state is entered. In any event, since the engine is not running in the PAUSE state, vehicle emissions, such as carbon dioxide emissions, can be reduced in order to provide a more efficient system per journey.
In the PAUSE state, while the engine is not running, some vehicle systems may continue to be active. These vehicle systems would not normally be active in the OFF state. Therefore there is some additional power consumption in the PAUSE state relative to the OFF state. Another distinction between the PAUSE state and the OFF state is that it is usually necessary for a user (driver) to activate the ignition key (or other equivalent mechanism) in order to move from the OFF state to the ON state or from the ON state to the OFF state. This is not the case when moving to or from the PAUSE state—instead, a vehicle controller (or other equivalent mechanism) makes a decision, usually based upon predetermined factors as discussed above, as to whether or not to enter the PAUSE state or leave the PAUSE state. This decision is automatic and does not require user input (e.g. turning of a key, pressing of a button, etc.).